Atrial fibrillation is an irregular heart rhythm that adversely affects approximately 2.5 million people in the United States. It is believed that at least one-third of all atrial fibrillation originates near the ostium of the pulmonary veins. Anatomically, two pairs of pulmonary veins are connected to the left atrium of the heart with each pair delivering blood to the heart from one of a patient's lungs. Accordingly, one technique to treat atrial fibrillation includes the formation of circumferential lesions around the ostia where a pulmonary vein connects with the left atrium. Forming a conduction block, via tissue ablation, can inhibit the transmission of irregular electrical signals responsible for inducing an arrhythmia. However, to be most effective, a relatively deep, uniform lesion is preferred.
Cryoablation is one method for creating the circumferential lesions that block the conduction of irregular signals through the pulmonary vein. In one type of cryoablation procedure, a balloon is positioned within the ostia of the pulmonary vein, thereby creating a seal. The balloon may contain an ablation fluid that is gaseous or liquid, such as saline, nitrous oxide, or perfluorocarbon. Typically, the ablation fluid cools tissue in contact with the outer surface of the balloon to a temperature that destroys cells. This disables the transmission of the irregular signals responsible for atrial fibrillation. It should also be noted that cryoablation procedures can treat other conditions such as stenosis.
Another type of cryoablation procedure involves treating the ostium tissue with a separate cryoablation member located outside the balloon. The cryoablation member can freeze the tissue by directly touching the tissue or by spraying the tissue with a coolant, depending on the approach.
While such procedures have proven effective, further improvements, particularly regarding positioning of ablation devices relative to an anatomic structure, would be beneficial.